The FOC flat field images applied to all FOC data during standard 'pipeline' processing have been heavily smoothed to reflect large scale response variations only. Small scale features are not removed during this step. The two images are external flat fields using the Orion Nebula in the ultraviolet as a nearly featureless source. Both are full-format, 1024 by 1024 pixels. They have been geometrically corrected and flat-fielded. The purpose of these is to show the locations of reseau marks, scratches, and other features inherent in FOC images.
When comparing these images with others, bear in mind that the geometric distortion varies somewhat with time, so feature locations will not match perfectly. These images were created from geometrically corrected flat field images taken prior to the installation of COSTAR. As a result, post-COSTAR images will not align to these images due to the different optical distortion of the COSTAR corrected images. An unsmoothed flat field is now available for comparison to COSTAR-corrected FOC images. This flat-field was corrected using the latest geometric correction which will make comparison with post-COSTAR images straight-forward.
The following images are available in FITS format: